The present invention relates to an apparatus and a method for semiconductor wafer yield enhancement, and more particularly to a semiconductor wafer test yield enhancement that integrates a defect detection and characterization system, and a defect eradication system.
Surface cleaning of a semiconductor wafer has a significant bearing on device test yields. As the semiconductor industry pushes for smaller integrated circuit (IC) dimensions, e.g., 0.35 micron, 0.25 micron and 0.1 micron, the defect density level and size of the smallest particle capable of causing a failure in an IC decrease, as well. For example, for IC devices of 0.35 microns or less particles of the order of one third of the device size, i.e., 0.12 micron or less can cause the circuit to malfunction. Moore""s Law projects that by 2005 IC devices will have over 700 million transistors per chip (FIG. 1). The Semiconductor Industry Association (SIA) Roadmap projects that the 0.115 micron/300 millimeter wafer technology generation in 2005 will require a very low defect level of only 1260 defects per millimeter square for robust test yields.
Table 1 illustrates the effect of defect density level on test yield for several 0.18 micron products. For a 1 Gigabit dynamic RAM (DRAM) memory a decrease in defect density from 0.10 Defects/cm2 to 0.01 Defects/cm2 increases the device process yield from 12% to 81%. Similar yield increases are observed in a 1000 MIP Microprocessor and a System on a Chip (SOC) device. The results of Table 1 are included in an internal report presented to Applied Materials by Dr. Wayne Ellis and Paul Castrucci, entitled xe2x80x9cAMAT Scenario 2003-IC Yield Analysisxe2x80x9d October 1998, incorporated herein by reference.
The IC industry needs technology tools that will eradicate defects in order to achieve the very low defect levels required to produce products with very fine feature sizes while maintaing commercially viable wafer processes with high test yields.
Surface defects of an IC include surface structural disorders and discrete pieces of matter that range in size from submicron dimension to granules visible to observation with the eye. Surface structural disorders include microscratches, metal etching stringers, missing contacts, and bridging due to tungsten residue during chemical mechanical polishing (CMP). Discrete pieces of matter may be fine dust, dirt particles, foreign molecules including carbon, hydrogen, and/or oxygen. Particulate contaminants (xe2x80x9cparticulatesxe2x80x9d) frequently adhere to a surface by weak covalent bonds, electrostatic forces, van der Waals forces, hydrogen bonding, coulombic forces, or dipole-dipole interactions, making removal of the particulates difficult. Particulates frequently encountered in practice include polysilicon slivers, photoresist particles, metal oxide particles, and slurry residue. It is known that not all particulates are equally undesirable. For example, particulates that adhere at some non-sensitive portions of the IC circuitry may have no effect on operation or performance, and need not necessarily be removed (xe2x80x9cdon""t caresxe2x80x9d). On the other hand, particulates that adhere to active areas or critical locations (xe2x80x9ckiller defectsxe2x80x9d) can cause failure of the IC circuitry and must be removed for proper operation.
Semiconductor surface cleaning technology involves breaking the above mentioned adhesion bonds and removal of the contaminants. The known methods of semiconductor surface cleaning include chemical wet-processes, e.g. RCA and Piranha etch, chemical dry-processes, mechanical processes, thermal, ultrasonic, optical techniques and combinations thereof. The chemical wet-processes require large amounts of chemical solutions and water. These chemical solutions are expensive, frequently introduce new contaminants, and their disposal causes an environmental problem. Thermal processes require in some cases melting of the top surface and removal via ultra high vacuum pressure. The melting of the top layer may disturb the integrity of the previously deposited layers and the high vacuum equipment are both expensive and time consuming to operate. Thermal annealing does not require melting of the top surface. However, it requires longer exposure to temperatures below the melting point, which may cause undesired diffusion of particles and changes of the crystalline structure.
Gas-phase chemical dry-cleaning processes have been used for years to clean semiconductor surfaces. Among the various chemical dry-cleaning processes, the supercritical fluid cleaning process offers many advantages.
At temperatures above 31xc2x0 C. and pressure of 1072 psi, the liquid and gaseous phases of CO2 combine to form supercritical CO2 (SCCO2). Supercritical fluid possesses liquid-like solution and gas-like diffusion properties. SCCO2 has low viscosity and low dielectric constant. The low viscosity of SCCO2 enables rapid penetration into crevices, pores, trenches and vias with complete removal of both organic and inorganic contaminants. Organic contaminants that can be removed with SCCO2 include oils, grease, organic films, photoresist, plasticizers, monomers, lubricants, adhesives, fluorinated oils and surfactants. Inorganic contaminants that can be removed with SCCO2 include metals, metal complexing agents, inorganic particulates. Contaminants solvate within the SCCO2 and are evacuated into a low pressure chamber, where they become insoluble and are precipitated from the liquid CO2. The supercritical fluid technology cleaning tool SCF-CT apparatus has a small footprint of about 75 square feet and sells for about $500K to $1M. Conventional water clean benches cost over $2M. The process of cleaning semiconductor surfaces using SCCO2 is described in a technical paper entitled xe2x80x9cPrecision Cleaning of Semiconductor Surfaces Using Carbon Dioxide Based Fluidsxe2x80x9d by J. B. Rubin, L. D. Sivils, and A. A. Busnaina published in Proceedings SEMICON WEST 99, Symposium On Contamination Free Manufacturing for Semiconductor Processing, San Francisco, Calif. Jul. 12-14, 1999, the entire content of which is expressly incorporate herein by reference.
While cleaning of semiconductor surfaces with SCCO2 has proven to be effective for removing particles, improved cleaning results are required before this process can become commercially successful. In particular, an intelligent cleaning system that incorporates defect diagnostics, optimal cleaning based on SCF-CT unique parameters, and defect eradication is desirable.
In general, in one aspect, the invention features a semiconductor wafer processing apparatus including equipment for identifying and characterizing surface defects on each wafer at at least one processing station and for creating a record of the surface defect data for each wafer and equipment for performing supercritical fluid cleaning of the wafers. The equipment for supercritical cleaning is adapted to receive the surface defect data from the created record and apply a supercritical fluid cleaning recipe based on the surface defect data. The apparatus further includes equipment for transferring a plurality of semiconductor wafers among a plurality of processing stations under computer control and equipment for transferring of cleaned wafers to an output station.
Implementations of this aspect of the invention may include one or more of the following features. The surface defect identification and characterization data may include position coordinates, type, density and size of surface defects on each wafer. The equipment for identifying and characterizing surface defects on each wafer may be an advanced patterned wafer inspection system with an automatic defect classification program. The advanced patterned wafer inspection system with an automatic defect classification program may be a COMPASS(trademark) system with On-The-Fly Automatic Defect Classification (OTF(trademark)-ADC). The supercritical fluid cleaning recipe may be a generic recipe. The generic recipe may includes placing the wafers in a pressure chamber, introducing a gas that undergoes a supercritical transition into the pressure chamber, setting temperature and pressure condition in the pressure chamber to produce a supercritical fluid on the surface of the wafers and exposing the wafers for a predetermined time to the supercritical fluid. The supercritical fluid may be carbon dioxide and the temperature and pressure condition may range from 20 to 70xc2x0 C. and 1050 to 10000 psi, respectively. The supercritical fluid may also be carbon monoxide, argon, nitrogen, helium, xenon, nitrous oxide, ethane, and propane. The supercritical fluid cleaning recipe may be a defect specific recipe. The defect specific recipe may include placing the wafers in a pressure chamber, introducing a gas that undergoes a supercritical transition into the pressure chamber, setting temperature and pressure condition in the pressure chamber to produce a supercritical fluid on the surface of the wafers, introducing a defect specific co-solvent into the pressure chamber creating a mixture of supercritical fluid with the defect specific co-solvent, and exposing the wafers for a predetermined time to the mixture. The defect specific co-solvent may be methanol, isopropyl alcohol and other related alcohols, butylene carbonate, propylene carbonate and related carbonates, ethylene glycol and related glycols, ozone, hydrogen fluoride and related fluorides, ammonium hydroxide and related hydroxides, citric acid and related acids and mixtures thereof. The volume ratio of the defect specific co-solvent to the supercritical fluid may be within the range of 0.001 to 15 percent.
The semiconductor processing apparatus of this aspect of the invention may further include equipment for identifying and locating specific stubborn defects with respect to their position coordinates and for updating the data records for any surface cleaned wafer. The equipment for locating specific stubborn defects may be a scanning electron microscope, an optical microscope, or an atomic force microscope. The apparatus of this aspect of the invention may further include equipment for performing an elemental chemical analysis of the specific stubborn defects. The equipment for performing a chemical analysis may be a mass spectrometer, a secondary ion mass spectrometer, a Raman spectrometer, an optical spectrometer, or an Auger spectrometer. The apparatus of this aspect of the invention may further include a database storing supercritical fluid cleaning recipe data. The supercritical fluid cleaning recipe data may include generic and defect specific recipes.
In general, in another aspect, the invention features a semiconductor wafer processing apparatus including equipment for identifying and characterizing surface defects on each wafer at at least one processing station and for creating a record of the surface defect data for each wafer at the processing station. The apparatus further includes equipment for performing supercritical fluid cleaning of the wafers. The equipment for supercritical fluid cleaning is adapted to receive the surface defect data from the record and apply a supercritical fluid cleaning recipe based on the surface defect data. The apparatus may further include equipment for identifying and locating specific stubborn defects with respect to their position coordinates and for updating the surface defect data records for any surface cleaned wafers and equipment for performing an elemental chemical analysis of the specific stubborn defects and for updating the surface defect data records for any surface cleaned wafers. The apparatus may further include equipment for performing a defect specific supercritical cleaning of the wafers to eradicate the specific stubborn defects. The equipment for defect specific supercritical cleaning is adapted to receive the updated surface defect data from the record and apply a defect specific supercritical fluid cleaning recipe. The apparatus further includes equipment for transferring a plurality of semiconductor wafers among a plurality of processing stations under computer control and equipment for transferring of cleaned wafers to an output station.
In general, in another aspect, the invention features a semiconductor wafer processing apparatus including a database storing supercritical fluid cleaning recipe data for at least one processing station, and equipment for performing supercritical fluid cleaning of the wafers at the at least one processing station. The equipment for supercritical cleaning is adapted to receive supercritical fluid cleaning recipe data from the database. The apparatus further includes equipment for transferring a plurality of semiconductor wafers among a plurality of processing stations under computer control and equipment for transferring of cleaned wafers to an output station.
In general, in another aspect, the invention features a method for semiconductor wafer processing including identifying and characterizing surface defects on each wafer at at least one processing station and creating a record of the surface defect data for each wafer at the at least one processing station. Next the surface defect data and the wafers are transferred to a supercritical fluid cleaning apparatus. Next a supercritical fluid cleaning of the wafers takes place. The supercritical fluid cleaning apparatus is adapted to apply a supercritical fluid cleaning recipe based on the surface defect data. The method further includes transferring a plurality of semiconductor wafers among a plurality of processing stations under computer control in a predetermined sequence starting at an input station and ending at an output station and finally transferring of the cleaned wafers to an output station.
In general, in another aspect, the invention features a semiconductor wafer processing method including first identifying and characterizing surface defects on each wafer at at least one processing station and creating a record of the surface defect data for each wafer at the at least one processing station. Next the surface defect data and the wafers are transferred to a supercritical fluid cleaning apparatus where a supercritical fluid cleaning of the wafers takes place. The supercritical fluid cleaning apparatus is adapted to apply a supercritical fluid cleaning recipe based on the surface defect data. Next specific stubborn defects are identified and located with respect to their position coordinates and the surface defect data records for any surface cleaned wafers are updated. Next an elemental chemical analysis of the specific stubborn defects takes place and the surface defect data records for any surface cleaned wafers are updated. The updated surface defect data are transferred to the supercritical fluid cleaning apparatus where a defect specific supercritical cleaning of the wafers is performed to eradicate the specific stubborn defects. The supercritical fluid cleaning apparatus is adapted to apply a defect specific supercritical fluid cleaning recipe based on the updated surface defect data. The method further includes transferring a plurality of semiconductor wafers among a plurality of processing stations under computer control in a predetermined sequence starting at an input station and ending at an output station and finally transferring of the cleaned wafers to an output station.
In general, in yet another aspect, the invention features a semiconductor wafer processing method including storing supercritical fluid cleaning recipe data for at least one processing station in a database. The supercritical fluid cleaning recipe data are transferred from the database to a supercritical fluid cleaning apparatus. The wafers are also transferred to the supercritical fluid cleaning apparatus where a supercritical fluid cleaning of the wafers takes place. The supercritical fluid cleaning apparatus is adapted to apply the supercritical fluid cleaning recipe. The method further includes transferring a plurality of semiconductor wafers among a plurality of processing stations under computer control in a predetermined sequence starting at an input station and ending at an output station and finally transferring of the cleaned wafers to an output station.
Among the advantages of this invention may be one or more of the following. The yield enhancement system (YES) of this invention enables the production of wafers with defect levels of 0.01 defects/cm2 or less. This low defect level translates in significant IC test yield increases. Many semiconductor cleaning applications can be handled by the SCF-CT. The YES system has a significantly smaller footprint and costs less than the traditional wet-chemical process stations. The YES system of this invention is compatible with the small device dimensions and test yield requirements necessary to advance the IC fabrication process in the future. At defect densities of 0.12 defects/cm2 and lower water based wafer cleaning becomes ineffective. The YES system of this invention is a technology enabler for achieving defect densities of 0.03 defects/cm2 and lower. Furthermore, the YES system of this invention produces an economic benefit of the order of several billion dollars in wafer production of 1000 wafer starts per day over the period of one year. Referring to Table 1, the YES system of this invention can produce a SOC wafer with 52 potential dies, a defect level of 0.01 defects/cm2 and a corresponding yield of 64%. The 64% test yield of the 52 die-SOC translates into 33 good dies. Assuming a price of $1000.00 per die and a daily production of 1000 good wafers this translates to $33 million dollars per day or $10 billion dollars per year in good SOC dies. Similarly, for the same SOC wafer with 52 dies at a defect level of 0.04 defects/cm2 and a corresponding yield of 12% we get $2 billion per year of good dies. Therefore, the YES system of this invention enables us to capture a revenue potential of $8 billion per year on SOC wafer production.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and description below. Other features, objects and advantages of the invention will be apparent from the following description of the preferred embodiments, the drawings and from the claims.